Enabling custom Tectonic Identity TLS certificates

The module does not contain any logic, but just passes user provided certificates from its input directly to its output. This is to prevent changing existing references to the tls/identity/self-signed module, hence all tls/identity/* modules share the same outputs.

This certificate is used by Tectonic Console to communicate with Tectonic Identity's gRPC endpoint, securing communication between Console and the Tectonic Identity. The gRPC endpoint is provided for use in revoking tokens. Securing this channel ensures that tokens generated for cluster access are always secured.